Ferns for Terrariums: The Best Varieties for Beginners

Ferns and terrariums are a natural pairing. Most ferns evolved in the shaded, humid understory of forests, which is almost exactly the environment a well-built terrarium recreates in miniature. That said, some ferns are considerably easier to start with than others, particularly if you're building your first closed or semi-closed container, and getting the pairing of fern and vessel right up front saves a lot of trial and error later.

Boston fern

One of the most widely grown houseplant ferns, and for good reason: it tolerates a fairly wide range of humidity, which makes it forgiving while a new terrarium's conditions stabilise. Its fronds arch outward in a full, feathery shape, so it works well as a taller centerpiece plant rather than tucked into a corner. It does need reasonably frequent watering compared with some of the plants on this list, so it's better suited to an open terrarium or a closed one you check on regularly. A mature Boston fern's arching fronds can spread 40–50cm across in open ground, but kept in a terrarium's confined root space and trimmed periodically it typically holds to something closer to 15–20cm — still the largest footprint on this list, so it tends to work best as a single centerpiece rather than one of several ferns in a small jar.

Maidenhair fern

Prized for its delicate, almost lacy fronds on thin dark stems, maidenhair fern is more particular about consistent humidity than the Boston fern, and dry air will brown its fronds quickly. That pickiness is exactly why it's such a good closed-terrarium plant — the stable, high humidity behind a sealed lid is precisely what it wants, and it rewards that consistency with some of the most delicate foliage of any common terrarium plant. It stays compact in a terrarium setting, usually somewhere in the 12–18cm range, which makes it easy to pair with a taller companion plant without either one crowding the other.

Bird's nest fern

Instead of the classic feathery fronds, bird's nest fern grows broad, wavy-edged leaves in a rosette shape, giving a terrarium a very different texture from the other plants on this list. It's an epiphyte in the wild, often growing on trees rather than in soil, which makes it naturally tolerant of the free-draining substrate a terrarium needs. It handles a range of humidity reasonably well, making it a flexible choice for either open or closed builds, and a young plant's rosette typically holds to a 15–20cm spread for a long stretch before it needs more room.

Table fern

A compact, upright fern that stays relatively small and tidy, table fern is a good choice when floor space is limited — a small jar or narrow-necked vessel that can't accommodate a wide, arching Boston fern can often still fit a table fern comfortably. It appreciates the same humid, indirect-light conditions as most terrarium ferns and doesn't ask for much beyond that, and its mature spread of roughly 10–15cm is the smallest of the four, making it the easiest to fit two or three of into a single mid-sized jar.

A note on toxicity

All four of these are true ferns, and true ferns are generally considered non-toxic to cats and dogs — genuinely good news for a plant family this common in homes with pets. It's worth knowing the one mix-up that trips people up here: "asparagus fern" (Asparagus setaceus or A. densiflorus) is a popular houseplant that isn't a true fern at all despite the name, and it is considered toxic to cats and dogs if chewed, along with causing skin irritation in some people who handle it. If you're shopping for terrarium ferns and asparagus fern comes up as a similar-looking option, it's worth knowing it doesn't belong in the same "generally safe" category as the four covered here. As with any houseplant in a home with pets or small children, a plant sitting at easy reach on a shelf or coffee table is worth a quick check before it comes home, and a vet or poison control line is the right call if a chewed plant is ever a concern. A quick way to tell a true fern from a lookalike at the shop: true ferns unroll new growth from a tightly coiled "fiddlehead," a shape asparagus fern's needle-like foliage doesn't share, and true ferns reproduce by spores rather than flowers or seeds — a small distinction, but a useful one if the label on a plant isn't clear.

General care that applies to all of them

Every fern on this list shares a few preferences: bright, indirect light rather than direct sun (which will scorch fronds fast behind glass), consistently moist but not waterlogged substrate, and still, humid air. None of them are picky about soil pH or fertiliser in a terrarium setting — a standard terrarium or fern-specific potting mix suits all four. If you do fertilise, a light, well-diluted feed every month or two during active growth is plenty; terrarium ferns are chosen for slow, contained growth in the first place, and a stronger feeding schedule meant for an outdoor bed tends to push growth faster than a sealed glass footprint can comfortably absorb.

Where they differ most is tolerance for lower humidity and less frequent attention. If you're building an open terrarium you'll check often, Boston fern and bird's nest fern are the more forgiving starting points. If you're building a sealed jar you'd rather leave mostly alone, maidenhair fern will reward the stable humidity with its finest, most delicate growth.

Fitting ferns to your container: a worked example

Spread matters more than most beginners expect when it's time to actually plant, because a fern's mature footprint is usually much larger than the small starter plant it arrives as. Take a mid-sized rectangular tank with a 30 x 20cm floor — 600cm² of growing space. Planted at a "moderate" density (leaving reasonable breathing room between plants rather than packing them edge to edge), that floor comfortably fits around four ferns at table fern's roughly 10cm mature spread, but only about two at maidenhair's 15cm spread, and typically just one true centerpiece plant once you're working with Boston fern's larger mature footprint. A "sparse" density — useful if you want obvious room for the plants to fill in over the following months — drops those counts further still. Running your own container's floor area and each fern's realistic mature spread through the plant count calculator on this site gives an exact number rather than an eyeballed guess, and it's worth doing that calculation using the mature spread, not the size the plant arrives at, since planting to the day-one size is the single most common way a terrarium ends up overcrowded within a year.

Pairing ferns with moss and other plants

Ferns and moss share close to identical humidity and light preferences, which makes them one of the easiest terrarium pairings to get right — a moss carpet at a fern's base does real work beyond decoration, holding surface moisture that benefits the fern's shallow feeder roots and keeping the substrate from crusting dry between waterings. Cushion moss around the base of a table fern or maidenhair fern is a common, reliable combination for exactly this reason.

Where pairings go wrong is usually a watering mismatch rather than a light or humidity one. All four ferns on this list want consistently moist, never waterlogged substrate, which fits comfortably alongside moss but clashes badly with succulents or air plants that need to dry out between waterings — a good reason to keep ferns to closed or consistently humid open builds rather than mixing them into a display built around drought-tolerant plants.

Watering and the overwatering trap

Fern roots are more sensitive to sitting in waterlogged substrate than their lush, moisture-loving reputation might suggest — it's consistently damp air around the fronds they want, not permanently soaked soil around the roots. Substrate that's kept too wet for too long, especially in a closed terrarium with a shallow or under-built drainage layer, is a common way to lose a fern to root rot even though the plant looked perfectly suited to the humid setup on paper. It's also the same overly damp, poorly ventilated condition that invites mould and fungus gnats, so the fix for both problems tends to be the same: more airflow (a longer lid-off airing, more often), not more water, and letting the substrate surface come up to a light dampness rather than staying visibly wet between waterings.

Keeping a fern in bounds

All four of these ferns will eventually grow past the size they arrived at, and a terrarium is a fixed space, so a little grooming keeps things in proportion. Snipping off a browning or damaged frond at its base, rather than partway along the stem, keeps the plant looking tidy without leaving a stub behind. If a fern's root ball genuinely outgrows the space it was given, dividing it and replanting a smaller section is usually more successful than trying to squeeze the whole original plant into an unchanged footprint.

Whichever fern you choose, it's worth working out how many will comfortably fit your container before you buy, since ferns' fronds spread out considerably wider than the small starter plant you bring home. The plant count calculator on this site estimates how many will fit your floor area at a sparse, moderate, or full planting density based on the plant's mature spread.